SELF AWARENESS: THE LAST FRONTIER

One of the last remaining problems in science is the riddle of consciousness. The human brain—a mere lump of jelly inside your cranial vault—can contemplate the vastness of interstellar space and grapple with concepts such as zero and infinity. Even more remarkably it can ask disquieting questions about the meaning of its own existence. "Who am I" is arguably the most fundamental of all questions.

It really breaks down into two problems—the problem of qualia and the problem of the self. My colleagues, the late Francis Crick and Christof Koch have done a valuable service in pointing out that consciousness might be an empirical rather than philosophical problem, and have offered some ingenious suggestions. But I would disagree with their position that the qualia problem is simpler and should be addressed first before we tackle the "Self." I think the very opposite is true. I have every confidence that the problem of self will be solved within the lifetimes of most people reading this column. But not qualia.

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V.S. RAMACHANDRAN, a neuroscientist, is Director, Center for Brain and Cognition, University of California, San Diego; Author, A Brief Tour of Human Consciousness, and coauthor, Phantoms in the Brain.

[V.S. RAMACHANDRAN:] One of the last remaining problems in science is the riddle of consciousness. The human brain—a mere lump of jelly inside your cranial vault—can contemplate the vastness of interstellar space and grapple with concepts such as zero and infinity. Even more remarkably it can ask disquieting questions about the meaning of its own existence. "Who am I" is arguably the most fundamental of all questions.

It really breaks down into two problems—the problem of qualia and the problem of the self. My colleagues, the late Francis Crick and Christof Koch have done a valuable service in pointing out that consciousness might be an empirical rather than philosophical problem, and have offered some ingenious suggestions. But I would disagree with their position that the qualia problem is simpler and should be addressed first before we tackle the "Self." I think the very opposite is true. I have every confidence that the problem of self will be solved within the lifetimes of most readers of this essay. But not qualia.

The qualia problem is well known. Assume I am an intellectually highly advanced, color-blind martian. I study your brain and completely figure out down to every last detail what happens in your brain—all the physico-chemical events—when you see red light of wavelength 600 and say "red". You know that my scientific description, although complete from my point of view, leaves out something ineffable and essentially non-communicable, namely your actual experience of redness. There is no way you can communicate the ineffable quality of redness to me short of hooking up your brain directly to mine without air waves intervening (Bill Hirstein and I call this the qualia-cable; it will work only if my color blindness is caused by missing receptor pigments in my eye, with brain circuitry for color being intact.) We can define qualia as that aspect of your experience that is left out by me—the color-blind Martian. I believe this problem will never be solved or will turn out (from an empirical standpoint) to be a pseudo-problem. Qualia and so-called "purely physical" events may be like two sides of a Moebius strip that look utterly different from our ant-like perspective but are in reality a single surface.

So to understand qualia, we may need to transcend our ant-like view, as Einstein did in a different context. But how to go about it is anybody's guess.

The problem of self, on the other hand, is an empirical one that can be solved—or at least explored to its very limit—by science. If and when we do it will be a turning point in the history of science. Neurological conditions have shown that the self is not the monolithic entity it believes itself to be. It seems to consist of many components each of which can be studied individually, and the notion of one unitary self may well be an illusion. (But if so we need to ask how the illusion arises; was it an adaptation acquired through natural selection?)

Consider the following disorders which illustrate different aspects of self.

• Out of body experiences: patients with right fronto-parietal strokes report floating out into space watching their body down below—undoubtedly contributing to the myth of disembodied souls. Left hemisphere strokes result in the feeling of a mysterious presence—a phantom twin—hovering behind the patient's left shoulder.

• Apotemnophilia: An otherwise completely normal person develops an intense desire to have his arm or leg amputated. The right parietal (a part of it known a SPL) normally contains a complete internal image of the body. We showed recently that in these patients the part of the map corresponding to the affected limb is congenitally missing, leading to alienation of the limb.

The patients are sometimes sexually attracted to amputees, We postulate that in " normal" individuals there is a genetically specified homunculus in S2 that serves as a template acting on limbic and visual areas to determine aesthetic preference for ones own body type. Hence pigs are attracted to pigs not people. (Which is not to deny an additional role for olfactory and visual imprinting) But if the image in S2 is missing a limb this may translate into an aesthetic preference toward an amputee - mediated by reverse projections that are known to connect the ("emotional") amygdala to every stage in the visual hierarchy.

• Transsexuality; A woman claims that for as far back as she can remember she felt she was a man trapped in a woman's body—even experiencing phantom penises and erections. Our ordinary notion of every person having a single sexual identity (or self) is called into question. It turns out there are at least four distinct aspects of sexuality; your external anatomy, your internal brain-based body image, your sexual orientation and your sexual identity—who you think others think of you as. Normally these are harmonized in fetal development but if they get uncoupled you become a transsexual person. (It is important to note there is nothing "abnormal" about them, any more than you would regard being gay as abnormal.)

• A patient with a phantom arm simply watches a student volunteer's arm being touched. Astonishingly the patient feels the touch in his phantom. The barrier between him and others has been dissolved.

• Cotards syndrome; the patient claims he is dead and rejects all evidence to the contrary.

• Capgras delusion; the patient claims that his mother looks like his mother but is in fact an imposter. Other patients claim that they inhabit a house that's a duplicate of their real house. Bill Hirstein and I (and Haydn Ellis and Andrew Young) have shown that this highly specific delusion arises because the visual area in the brain is disconnected from emotional areas. So when our patient David sees his mother he recognizes her—along with the penumbra of memories linked to her. But no emotions and no jolt of familiarity is evoked so he rationalizes away his curious predicament saying she is an imposter. It is important to note that these patients are usually intelligent and mentally stable in most other respects. It is the selective nature of the delusion that makes it surprising and worth studying.

David also had difficulty abstracting across successive encounters of a new person seen in different contexts to create an enduring identity for that person. Without the flash of recognition he ought to have experienced in the second, third or n'th exposure, he couldn't bind the experiences together into a single person. Even more remarkably David sometimes duplicated his own self! He would often refer to "The other David who is on vacation." It was as if even successive episodes of his own self were not bound together the way they are in you and me.

This is not to be confused with MPD ("multiple personality disorder") seen in psychiatric contexts. MPD is often a dubious diagnosis made for medico-legal and insurance purposes and tends to fluctuate from moment to moment. (I have often been tempted to send two bills to an MPD patient to see if he pays both.) Patients like David, on the other hand, may give us genuine insight into the neural basis of selfhood.

• In another disorder the patient, with damage to the anterior cingulate
develops "akinetic mutism". He lies in bed fully awake and alert but cannot talk or walk—indeed doesn't interact in any way with people or things around him. Sometimes such patients wake up (when given certain drugs ) and will say "I knew what was going on around me but I simply had no desire to do anything ". It was if he had selective loss of one major attribute of the self— free will".

• Even odder is a phenomenon called "The telephone syndrome". The patient (I'll call him John) will display akinetic mutism—no visual consciousness—when seeing his (say) father in person. But if he receives a phone call from his father he suddenly becomes conscious and starts conversing with him normally. (S. Sriram and Orrin Devinsky, personal communication.) It's as if there are two Johns—the visual John who is only partially conscious and the auditory John (with his own self) who talks over the phone. This implies a degree of segregation of selves—all the way from sensory areas to motor output—that no one would have suspected.

We will now consider two aspects of self that are considered almost axiomatic. First its essentially private nature. You can empathise with someone but never to the point of experiencing her sensations or dissolving into her (except in pathological states like folie a duex and romantic love). Second, it is aware of its own existence. A self that negates itself is an oxymoron. Yet both these axioms can fall apart in disease; without affecting other aspects of self. An amputee can literally feel his phantom limb being touched when he merely watches a normal person being touched. A person with Cotard's syndrome will deny that he exists; claiming that his body is a mere empty shell. Explaining these disorders in neural terms can help illuminate how the normal self is constructed.

To account for some of these syndromes we need to invoke mirror neurons discovered by Giacomo Rizzolatti, Victorio Gallase and Marco Iacoboni[2]. Neurons in the prefrontal cortex send out sophisticated signals down the spinal cord that orchestrate skilled and semi-skilled movements such as putting food in your mouth, pulling a lever, pushing a button, etc. These are "ordinary" motor command neurons but some of them, known as mirror neurons, also fire when you merely watch another person perform a similar act. It's as if the neuron (more strictly the network of which the neuron is part) was using the visual input to do a sort of "virtual reality simulation" of the other persons actions—allowing you to empathize with her and view the world from her point of view.

In a previous Edge essay[3] I also speculated that these neurons can not only help simulate other people's behavior but can be turned "inward"—as it were—to create second-order representations or metarepresentations of your own earlier brain processes. This could be the neural basis of introspection, and of the reciprocity of self awareness and other awareness. There is obviously a chicken-or-egg question here as to which evolved first, but that is tangential to my main argument. (See also Nick Humphrey's[4] contributions to Edge.) The main point is that the two co-evolved, mutually enriching each other to create the mature representation of self that characterizes modern humans. Our ordinary language illustrates this, as when we say "I feel a bit self conscious", when I really mean that I am conscious of others being conscious of me. Or when I speak of being self critical or experiencing "self-pity". (A chimp could—arguably—feel pity for a begging chimp, but I doubt whether it would ever experience self-pity.)

I also suggest that although these neurons initially emerged in our ancestors to adopt another's allocentric visual point of view, they evolved further in humans to enable the adoption of another's metaphorical point of view. ("I see it from his point of view" etc.) This, too, might have been a turning point in evolution although how it might have occurred is deeply puzzling.

There are also: "touch mirror neurons" that fire not only when your skin is touched but when you watch someone else touched. This raises an interesting question; how does the neuron know what the stimulus is? Why doesn't the activity of these neurons lead you to literally experience the touch delivered to another person? There are two answers. First the tactile receptors in your skin tell the other touch neurons in the cortex (the non-mirror neurons) that they are not being touched and this null signal selectively vetos some of the outputs of mirror neurons. This would explain why our amputee experienced touch sensations when he watched our student being touched; the amputation had removed the vetoing. It is a sobering thought that the only barrier between you and others is your skin receptors!

A second reason why your mirror neurons don't lead you to mime everyone you watch or to literally experience their tactile sensations might be that your frontal lobes send feedback signals to partially inhibit the mirror neurons' output. (It cant completely inhibit them; otherwise there would be no point having mirror neurons in the first place.) As expected, if the frontal lobes are damaged you do start miming people ("echopraxia").

Recent evidence suggests that there may also be mirror neurons for pain, disgust, facial expression—perhaps for all outwardly visible expression of emotions. (We call these "empathy" neurons or Gandhi neurons.) Some of these are in the anterior cingulate—others in the insula.

I mention these to emphasize that despite all the pride that your self takes in its individuality and privacy, the only thing that separates you from me is a small subset of neural circuits in your frontal lobes interacting with mirror neurons. Damage these and you "lose your identity"—your sensory system starts blending with those of others. Like the proverbial Mary of philosopher's thought experiments, you experience their qualia.

We suggest that many otherwise inexplicable neuro-psychiatric symptoms may arise from flaws in these circuits leading to "you-me" confusion and impoverished ego-differentiation. Lindsay Oberman, Eric Altschuler and I have seen strong preliminary hints that autistic children have a paucity of mirror neurons which would not only explain their poor imitation, empathy and 'pretend play" (which requires role-playing) but also why they sometimes confuse the pronouns I and You, and have difficulty with introspection. Even Freudian phenomena like "projection", seen in all of us, may have similar origins; "I love you" turns to "You love me" to make me feel safer.

Let us return to Cotards syndrome—the ultimate paradox of the self negating its own existence (sometimes claiming "I am dead", "I can smell my body rotting", etc.). We postulate that this arises from a combination of two lesions. First, a lesion that is analogous to Capgras but far more pervasive. Instead of emotions being disconnected from just visual centers, it is disconnected from all sensations and even memories of sensations. So the entire world becomes an imposter—unreal (not just the mother). Second, there may be dysfunctional interaction between the mirror neurons and frontal inhibitory structures leading to a dissolution of the sense of self as being distinct from others (or indeed from the world ). Lose the world and lose yourself—and it's as close to death as you can get. This is not a fully developed explanation by any means; I mention it only to indicate the style of thinking that we may need to explain these enigmatic syndromes.

Now imagine these same circuits become hyperactive as sometimes happens when you have seizures originating in the temporal lobes (TLE or temporal lobe epilepsy). The result would be an intense heightening of the patient's sensory appreciation of the world and intense empathy for all beings to the extent of seeing no barriers between himself and the cosmos—the basis of religious and mystical experiences. (You lose all selfishness and become one with God.) Indeed many of history's great religious leaders have had TLE. My colleague, the late Francis Crick, has suggested that TLE patients as well as priests may have certain abnormal transmitters in their brains that he calls "theotoxins". (He once told philosopher Pat Churchland that he had nothing against religion per se, so long as it was a private arrangement between consenting adults.)

I hasten to add that the involvement of the temporal lobes in mystical experiences does not in itself negate the existence of an abstract God, who, in Hindu philosophy, represents the supreme dissolution of all barriers. Perhaps the TLE patient has seen the truth and most of us haven't. I don't have TLE myself but have had personally had epiphanies when listening to a haunting strain of music, watching the aurora borealis, or looking at Jupiter's moons through a telescope. During such epiphanies I have seen eternity in a moment and divinity in all things. And, indeed, felt one with the Cosmos. There is nothing "true "or "false" about such experiences—they are what they are; simply another way of looking at reality.

Let us turn now to out-of-body experiences. Even a normal person—such as the reader—can at times adopt a "detached" allocentric stance toward yourself (employing something like mirror neurons) but this doesn't become a full blown delusion because other neural systems (e.g. inhibition from fontal structures and skin receptors ) keep you anchored. But damage to the right fronto-parietal regions or ketamine anesthesia (which may influence the same circuits) removes the inhibition and you start leaving your body even to the extent of not feeling your own pain. You see your pain "objectively" as if someone else was experiencing it. Some such opossum-like detachment also occurs in dire emergencies when you momentarily leave yourself and watch your body being raped or mauled by a lion. This reflex is normally protective (lying still to fool predators) but a vestige of it in humans may manifest as "dissociative" states under conditions of extreme stress.

The purported "unity" or internal consistency of self is also a myth. Most patients with left arm paralysis caused by right hemisphere stroke complain about it as, indeed, they should. But a subset of patients who have additional damage to the "body image" representation in the right SPL (and possibly insula) claim that their paralyzed left arm doesn't belong to them. The patient may assert that it belongs to his father or spouse. (As if he had a selective "Capgras" for his arm). Such syndromes challenge even basic assumptions such as "I am anchored in this body" or "This is my arm". They suggest that "belongingness" is a primal brain function hardwired through natural selection because of its obvious selective advantage to our hominoid ancestors. It makes one wonder if someone with this disorder would deny ownership of (or damage to) the left fender of his car and ascribe it to his mother's car.

There appears to be almost no limit to this. An intelligent and lucid patient I saw recently claimed that her own left arm was not paralyzed and that the lifeless left arm on her lap belonged to her father who was "hiding under the table". Yet when I asked her to touch her nose with her left hand she used her intact right hand to grab and raise the paralyzed hand—using the latter as a "tool" to touch her nose! Clearly somebody in there knew that her left arm was paralyzed and that the arm on her lap was her own, but "she"—the person I was talking to—didn't know. I then lifted her "father's hand" up toward her, drawing attention to the fact that it was attached to her shoulder. She agreed and yet continued to assert it belonged to her father. The contradiction didn't bother her.

Her ability to hold mutually inconsistent beliefs seems bizarre to us but in fact we all do this from time to time. I have known many an eminent theoretical physicist who prays to a personal God; an old guy watching him from somewhere up there in the sky. I might mention that I have long known that prayer was a placebo; but upon learning recently of a study that showed that a drug works even when you know it is a placebo, I immediately started praying. There are two Ramachandrans—one an arch skeptic and the other a devout believer. Fortunately I enjoy this ambiguous state of mind, unlike Darwin who was tormented by it. It is not unlike my enjoyment of an Escher engraving.

In the last decade there has been a tremendous resurgence of interest among neuroscientists in the nature of consciousness and self. The problem has been approached from many angles—ranging from single neuron electrophysiology to macroscopic brain anatomy (including hundreds of brain imaging studies ) What has been missing, though, is what might be called "psycho-anatomy"; whose goal is to explain specific details of certain complex mental capacities in terms of equally specific activity of specialized neural structures. As an analogy, consider the discovery of the genetic code. Crick and Watson unraveled the double helix, and saw in a flash that the complementarity of the two strands of the helix is a metaphor of the complementarity of parent and offspring in heredity. (Pigs give birth to pigs—not to donkeys.) In other words the structural logic of DNA dictates the functional logic of heredity. No such radical insight has emerged in neuroscience that would allow us to precisely map function on to structure.

One way of achieving this goal, as we have seen in this essay, might be to explore syndromes that lie at the interface between neurology and psychiatry Given the inherent complexity of the human brain, it is unlikely that there will be a single climactic solution like DNA (although I don't rule it out). But there may well be many instances where such a synthesis is possible on a smaller scale and these may lead to testable predictions and novel therapies. They may even pave the way for a grand unified theory of mind of the kind physicists have been seeking in trying to unify gravitation, relativity and quantum mechanics.

When such a theory finally emerges we can either accept it with equanimity or ask "Now that we have solved the problem of self, what else is there?"

Reality Club Discussion

V. S. Ramachandran's essay is another of his original and provocative contributions to neuropsychology and neurophilosophy, this time concerning self awareness, "the last frontier." In considering the related problems of qualia and self, he correctly observes that self is the more tractable research problem and presents an ingenious position based on neuropathological case studies and recent breakthroughs in neuroscience, including mirror neurons. To Ramachandran's list of the exotic, I suggest the addition of the mundane—tickle. Tickle provides an answer to his concluding statement, "Now that we have solved everything, what else is there? The answer is "other."

The starting point of my proposal is the observation that you cannot tickle yourself—tickle requires a non-self, animate entity on the surface of your skin. This non-self, animate other is the most primitive social stimulus. Self-produced cutaneous stimuli are not ticklish because our nervous system cancels their effects, perhaps in the cerebellum. In the absence of such cancellation, we would be constantly tickling ourselves by accident—the world would be filled with goosey people lurching their way through life in a chain-reaction of tactile false alarms.

The same mechanism that detects non-self, ticklish stimuli generates the sense of self. Although our sense of identity involves more than self/nonself discrimination, such a mechanism is at its foundation and a first step toward the evolution of personhood and the neurological computation of its boundaries. Pathology of the self/nonself discriminator may play a role in anomalous social behavior (e.g., touch aversion in autism) and body perception of the sort considered by Ramachandran. The computation of other also provides a bridge linking the often estranged disciplines of social psychology and neuroscience.

I, too, am enthusiastic about the potential of mirror neurons to explain many phenomena in the neurological, cognitive and social sciences, but I'm starting to suffer from a case of mirroritis, mostly from over-exposure. We are probably in the exuberant first stage of a three-stage process associated with scientific breakthroughs—unbridled optimism; subsequent, undue pessimism when unrealistic expectations are not met; and a final rebound to a more realistic level that reflects the actual value of a discovery.

The full importance of mirror process will be appreciated when the chain of events from sensory input to motor output is established and we can understand how a behavior is initiated, controlled and produced. So far, mirror neurons concern the disembodied neurological correlates of the action of others; they have not been shown to produce actual behavior. While we wait for these data, investigators lacking electrophysiological laboratories and fMRIs can explore mirror-like contagious acts such as yawning and laughing that are familiar to everyone, are associated with actual behavior, and are typically neglected by investigators of mirror neurons.

Biologist, Harvard University; author, The Social Conquest of Earth and The Creation: An Appeal to Save Life on Earth

Ramachandran has done it again, presenting fascinating case histories worthy of Ripley's Believe It or Not and extracting profound insights about the human mind. But there is a subtext to his essay (whether intended or not I don't know) that is alarming. The message seems to be that major puzzles about the mind—such as the nature of the "self"—will be solved by the field neuroscience. There is nary a mention of vast areas of research on the self from psychology, particularly social psychology, that have contributed much more to our understanding of the nature of the human self than neuroscience ever has or, in my opinion, ever will.

Here is a sampling is a sampling of key principles already established by social psychological research:

• The self is an inherently social construct, shaped by one's culture, family, and peers

• Introspection is severely limited. Much of the workings of the human mind, including attributes we generally think of as part of the "self," are unavailable to conscious scrutiny (note that this contradicts the premise that the study of the self is the same as the study of consciousness)

• The act of introspection can, depending on various well-known conditions, lead to long-term recovery from personal trauma or ill-advised choices that people later regret

• People observe their own behavior to deduce who they are

• The narratives people tell themselves are key determinants of their future behavior, regardless of whether these narratives are objectively true

Although the neurological underpinnings of these psychological phenomena would be interesting to explore, the phenomena themselves were not discovered by neuroscientists, and could not be easily deduced from neuroimaging or observations of brain-damaged patients. They required clever experimental manipulations and measurements of people's self-reports and behavior.

This isn't a horse race, of course. The "problem of the self" will not be solved by one subdiscipline alone. Studies of brain-damaged patients and images of the "normal" brain will teach us a lot, as will behavioral research. More progress will be made by combining these fields of inquiry than by focusing on one alone.

I love Rama. Such a wonderful writer, so provocative, so engaging. That said, I have to make a confession: I didn't get past the first sentence of this essay! In case you glossed it, here it is, word for word: "One of the last remaining problems in science is the riddle of consciousness." Really? One of the LAST problems in Science, capital S Science, as in not only psychology, but evolutionary biology, anthropology, and molecular biology, not to mention physics, and chemistry? Now that is a claim! Let's keep at bay all the unsolved problems in chemistry and physics, and focus instead on some a bit closer to psychology, say evolutionary biology. We still don't understand how sex evolved, really! There are several fascinating theories, but no concensus, and no knock down empirical evidence that lights the way. Here's another: are there non-carbon-based life forms? Maybe, but we don't know, yet. These are genuine problems, and like self-awareness, we are only beginning to have hints regarding their solutions.

Perhaps Ramachandran really meant to say that consciousness is one of the last remaining problems in the sciences of the mind, that is psychology and neurobiology. But that can't be right either. To take a problem near and dear, does anyone really believe that we have a genuine understanding of how the brain creates linguistic representations? If so, I would like to hear the account. But perhaps we shouldn't go for such a difficult problem.

How about an account of how the brain of a bee creates the representations of its own language, what von Frisch described in the 1960s as the bee's dance language. We certainly know that the dance is, in some respects, symbolic, in that it stands for or provides information about the location and quality of food. But we don't know how electrical activity creates this information in a format that can be read out and followed. And I don't think we are even close to understanding this problem. Scale it up, and ask how the brain creates the representations that enable us to appreciate the grammaticality of colorless green ideas sleep furiously, while also appreciating the lack of intelligible meaning, and we come up remarkably short.

None of this is to say that the problem of self-consciousness isn't a genuine problem, or that the material Ramachandran discusses isn't interesting. It is a problem, we don't have clear solutions, and studies of patient populations, such as individuals with Cotard's syndrome or Capgras, will certainly increase our understanding. All of this material is deeply fascinating (see, I did read past the first sentence), and in Rama's able hands, we will make terrific progress.

But even when we understand how the brain gives us an understanding of who we are, and how we experience the world, there will be many more problems left to solve. No scientist should fear the day when the problem of self-awareness is cracked. No scientist should think that they will be forced into early retirement [Leave it to our economy instead!]. No child should think that science is a dead end career because there are no more interesting problems to chew on. There are dozens and dozens of big problems to solve in every science, even the mind sciences. And the more learn, the more we create new problems. That is the beauty of science. That is the beauty of our ever inquisitive minds.

Marc Hauser is wise and scholarly; I always listen carefully to what he has to say. On this occasion he doesn't say much that I would disagree with. In fact he shows keen insight. He agrees with me that new insights into the nature of consciousness can come from studying the selective disturbances of different components of self that arise in neuropsychiatry. We believe this approach; mapping (not merely correlating) function on to structure, is analogous to mapping point mutations on to Chromosomes by Muller and Morgan (thereby linking chromosomes to heredity). The "monsters" he produced are analogous to neuropsychiatric syndromes. Another example is the discovery of homeotic mutants by Bateson in Drosophila ( legs replacing antennae)—anomalies which lived up to their promise of revolutionizing developmental and evolutionary biology long before the detailed nitty gritty mechanisms were figured out.

Yet even while applauding my enterprise, Hauser is uncomfortable with my opening line ("One of the last remaining problems in Science is the riddle of consciousness, etc.") and my closing sentence ("When such a theory finally emerges we can either accept it with equanimity or ask "Now that we have solved the problem of self, What else is there".) These were only intended to be playfully rhetorical (opening) and ironic (concluding) lines. Of course I don't mean that once we figure out Self, scientists will have nothing to do. Of course there are innumerable problems in every area of science to keep us busy for a long time. No one doubts that.

But if Hauser were to poll his colleagues in all sciences, asking them what the last remaining mysteries are, he would find that consciousness and self awareness on everyone's list. It doesn't follow that there wouldn't be plenty of other scientific problems in the list as well such as recursiveness in language, linking quantum mechanics with gravity, the viability of string theory, etc., but consciousness and the precise nature of time (in physics) would rank very near the top simply because we don't even know where to begin. It is precisely the fact that they seem to border on the metaphysical ("Who am I" or "Why does time have an arrow", etc.) that their solution in empirical terms would be especially exciting. I was certainly not trying to belittle other areas of research. What the "most important" problems are is a matter of taste; I know people who find counting the exact number of hair cells in the ear important and endlessly fascinating and I certainly wouldn't wish to deny them their privilege. On the other hand the question of which primates have "a theory of mind" (a topic which has been elegantly tackled by Hauser, Povinelli and others), is likely to be of interest to anyone who is not wholly devoid of common sense.

I have had this problem with Hauser before where he takes rhetorical or provocative opening lines literally, even while recognizing, by his own admission, that it has no bearing on either the spirit or the substance of my argument. Nonetheless, I welcome his suggestion that my concluding sentence could have been worded more carefully.

Psychologist, University of Massachusetts, Amherst; Author, The Cognitive Brain

There are certainly many remaining problems in science, but overwhelming evidence tells us that without our human brain as the source of our phenomenal experience (consciousness), science and all the questions of science would not exist. This is why understanding how the brain generates consciousness may be the most fundamental scientific problem. I doubt if Marc Hauser and Timothy Wilson actually believe that the pursuit of their scientific specialties and all the other scientific endeavors could have occurred without the evolution of the conscious human brain.

I have suggested that the hallmark of consciousness is a transparent representation of the world from a privileged egocentric perspective. The key questions of how the neuronal mechanisms and systems of our brain create the phenomenal experience of our self as the subjective origin of a surrounding world, and how we are able to parse and analyze the world to do our science are are now being addressed in a detailed neuronal model that relates our phenomenal experience of a personal world-space to our metaphorical theater of consciousness. Science must start within this phenomenal world.